We describe an instantaneous modal wave-front sensor. The sensor uses a Shack-Hartmann lenslet array to encode the wave-front distortion. A novel parallel electro-optic processor continuously converts the spot pattern to wave-front modes, e.g. Zernike polynomials, without a separate reconstructor. Using readily available components, the sensor can achieve MHz bandwidths for twenty modes. The bandwidth, sensitivity, and number of bits can vary for each mode to match the sensor to the disturbance in an optimal fashion. The proposed sensor has immediate application to beam control and turbulence sensing applications that require wide bandwidths. The measured wave-front modes can also be those of an adaptive optics system, directly providing control signals for the actuators of a deformable mirror. A similar electronic reconstructor mode is also described.
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